1. Field of the Invention
The present invention relates to a projector for projecting projection light on a projection object such as a screen and displaying an image, and in particular, relates to a projector equipped with a zoom lens with which the size of the projection light region for projecting projection light can be changed, and an imager for imaging a projection object.
2. Description of the Related Art
In recent years, a projector equipped with a zoom lens as the projection lens is known where the size of the projection light region formed on the screen can be freely varied by driving the zoom lens to change its zoom position.
Also, when such a projector is positioned in front of a screen, a variety of adjustments need to be made such as zoom adjustment, keystone correction, and focus adjustment on the projector in advance so the image is displayed correctly on the screen by the projection light projected by the projector onto the screen.
With portable projectors, however, the relative position to the screen may change each time the projector is set up, so the operator must make the above such adjustments each time, which is extremely troublesome.
As conventionally described in, for example, Japanese Patent Laid-Open Gazettes No. 2000-241874, when setting up a projector provided with a monitor camera in front of a screen, an adjustment pattern image formed on a liquid crystal light valve is projected on the screen so as to be displayed in an enlarged form, the screen displaying the pattern image is imaged by the monitor camera, the imaged image is analyzed, and the above-mentioned adjustments are carried out automatically based on the results of the analysis.
In general, a monitor camera is provided with a charge-coupled device (CCD) or the like for converting incoming light to electrical signals, and has a function (automatic exposure) for varying the shutter speed, gain (sensitivity), aperture, and the like to make the overall light of the imaged image a set value (exposure target value).
FIG. 8 is an explanatory view for describing the effects of the automatic exposure of a conventional monitor camera. In FIG. 8, the upper section shows a screen on which an adjustment pattern image is displayed, the middle section shows an imaged image objected by imaging the screen with a monitor camera, and the bottom section shows the value representing the brightness of each pixel lined up along the center horizontal line (dotted line) in the imaged image. Also, (A) shows the normal state of a projector, and (B) shows the state when the projector is set to low luminance.
Note that the value that shows the brightness of each pixel for the imaged image is called the gradation value hereafter. The concerned gradation value is a value that is obtained from image signals of the imaged image output from the monitor camera (CCD module).
In FIG. 8, the adjustment pattern image formed on a liquid crystal light valve is completely white, and as shown in the top section, the area where the pattern image is displayed on the screen. In further detail, the white portion area is the above-mentioned projection light area.
Also, the imaged image obtained by imaging with the monitor camera is as shown in the middle section.
Also, the horizontal axis corresponds to the position of each pixel in the center horizontal line of the projected image, and the vertical axis displays the gradient value for each pixel.
If the light source lamp in the projector is set to low luminance, the luminance of the projection light projected by the projector will be lower than normal. Because of this, the brightness of the pattern image displayed on the screen is darker in FIG. 8(B) than in (A). When the pattern image is imaged by the monitor camera using automatic exposure, however, the shutter speed, gain, aperture, and the like are adjusted such that the brightness of the entire imaged image is appropriate even if the photographic subject is dark, so the brightness of the pattern image of the imaged image is no different than normal for (A), as shown in FIG. 8(B). The black portion (that is, the portion outside the projected light region) in the projected image is thus dark enough to be ignored, so the gradient values for each pixel in the black portion will be considered 0, while the gradient value of nearly each pixel in the white portion (in other words, the pattern image portion) will be unchanged at the desired gradient value of Lt.
The automatic exposure function of the monitor camera operates in this manner, so that even if the source light lamp is set to low luminance, and the brightness of the pattern image displayed on the screen is dark, the gradient value of nearly each pixel in the white portion (in other words, the pattern image portion) of the imaged image can be maintained at the desired gradient value of Lt, as with normal luminance. This is not limited to a low luminance setting, but works similarly as the luminance drops when the light source lamp deteriorates over the passage of time.
In a projector equipped with such a zoom lens and monitor camera, however, problems such as those below occur due to automatic exposure of the monitor camera when the zoom position of the zoom lens is changed, changing the size of the projection light area on the screen.
FIG. 9 is an explanatory view for describing the problem due to automatic exposure of the monitor camera in conventional cases where the zoom position is changed. As in FIG. 8, in FIG. 9, the upper section shows a screen on which an adjustment pattern image is displayed, the middle section shows an imaged image of the screen, and the bottom section shows gradient values of the pixels in the imaged image. Also, (A) shows the state when the zoom position of the zoom lens is positioned centrally, (B) shows the state when the zoom position of the zoom lens is set to wide angle, and (C) shows the state where the zoom position of the zoom lens is set to telephoto.
If the zoom position of the zoom lens in the projector is set to wide angle, the area of the projected light region on the screen increases as shown in the top section of FIG. 9(B) compared to the central position in (A). Here, the adjustment pattern image formed on the liquid crystal light valve is fixed, so when the area of the projected light region increases on the screen, the pattern image displayed on the screen expands in accompaniment thereto. Consequently when the pattern image is imaged by the monitor camera, the area of the white portion (in other words, the pattern image portion) in the imaged image thus increases as shown in the center section of FIG. 9(B) compared to the central position of (A), and the area of the black portion (in other words, the portion outside the projected light region) decreases.
At this time, if the imaging is carried out with automatic exposure, the brightness of the overall imaged image is calculated as an exposure calculation value, which is controlled by the shutter speed, gain, aperture, and the like, such as to become equivalent to the exposure target value set beforehand. Here, the brightness of the overall imaged image is the sum of the amount of the light detected at each pixel with the CCD converted and amplified, of which the value is proportionate to the average value of the gradient value for each pixel in the imaged image. Thus, the average gradient value of all the pixels in the imaged image is used for the exposure calculated value.
Generally, the exposure target value is a fixed value set beforehand, so in cases where the zoom position is the central position as shown in FIG. 9(A), if the exposure calculation value matches the exposure target value, and the area of the white portion of the imaged image is made larger with the zoom position set to wide as described above, the average gradient value, that is, the exposure calculation value, of all the pixels will increase beyond the exposure target value by the amount that the area of the white portion was made larger. As a result, when the automatic exposure functions so as to change the shutter speed, gain, aperture, and the like such that the exposure calculation value is equivalent to the exposure target value, the average gradient value of all the pixels in the imaged image decreases. As described above, the black portion in the imaged image is black enough that it can be ignored, and the gradient value of each pixel therein is considered 0, so the decrease in the average gradient value of all the pixels is nothing more nor less than the gradient value of each pixel in the white portion decreasing below the desired gradient value Lt as shown in the bottom section of FIG. 9(B).
For a portion in an imaged image where, for example, the gradient values of the pixels are not 0 but are under a given threshold, said portion may be determined as being outside the projected light region, and the gradient values of the pixels in that portion replaced with zeros and the calculation made.
Alternatively, if the zoom position of the zoom lens is set to telephoto, the area of the projected light region on the screen is smaller as shown in the top section of FIG. 9(C) than the central position of (A). Here, the pattern image formed on a liquid crystal light valve is fixed as describe above, so when the area of the projected light region on the screen becomes smaller, the pattern image displayed on the screen shrinks along with it. When the pattern image is imaged by the monitor camera, then, the area of the white portion (in other words, the pattern image portion) in the imaged image becomes smaller as shown in the center section of FIG. 9(C) than the central position of (A), and the area of the black portion (in other words, the portion outside the projected light region) becomes larger.
When the area of the white portion in the imaged image thus becomes smaller, the average gradient value of all the pixels, that is, the exposure calculation value, decreases below the exposure target value by the amount that the area becomes smaller. As a result, when the automatic exposure functions so as to change the shutter speed, gain, aperture, and the like such that the exposure calculation value is equivalent to the exposure target value, the average gradient value of all the pixels in the imaged image rises, the result of which is that gradient value of each pixel in the white portion rises above the desired gradient value Lt as shown in the bottom section of FIG. 9(C).
As described above, conventionally, when the zoom position of the zoom lens is set to wide angle, and the area of the projected light region on the screen becomes large, the gradient value of each pixel in the white portion of the imaged image decreases below the desired gradient value Lt due to automatic exposure of the monitor camera, and conversely, when telephoto is used and the area of the projected light region becomes small, the gradient value of each pixel in the white portion increases above the desired gradient level Lt, so in neither case can the average gradient value of the white portion be maintained at the desired gradient level Lt.
Accordingly, if the average gradient value of the white portion in the imaged image thus deviates from the desired gradient value Lt due to a change in the zoom position of the zoom lens, the imaged image is analyzed as described above, and if various adjustments are to be carried out automatically based on the results of the analysis, there was the problem that appropriate adjustments could not be carried out depending on the content of the adjustments.
This sort of problem is not limited to cases where the adjustment pattern image is completely white, but may occur when the adjustment pattern is a different given color other than white (for example, green, or the like), and when the color is not over the entire surface but only a part of it.